Generating backwashable carbon nanotube mats on the inner surface of polymeric hollow fiber membranes

Porous carbon nanotube (CNT) mats adsorbed on flat sheet membranes have previously been shown to significantly improve fouling resistance and contaminant removal capabilities. Unfortunately, these CNT mats are easily disrupted by backwashing, severely limiting their value in commercial membranes. In this study, we describe how CNT mats, which are stable to backwashing, can be generated on the inner surface of hollow fiber membranes. Mat stability was determined from electron microscopy and by quantifying the mass of CNTs lost during aggressive backwashing, including hydraulic stress and exposure to harsh chemicals. Stable mats were also formed with powder activated carbon, demonstrating that the mat's stability is not a consequence of CNT properties, but rather the nature and directionality of the forces that these mats experience during backwashing. Compared to virgin membranes, CNT-modified membranes exhibited improved fouling resistance which was sustained through multiple backwashing cycles. Moreover, no measureable quantities of CNTs entered the permeate when natural organic matter was filtered through a CNT-modified membrane, indicating that CNTs will not be released into the permeate during filtration. Collectively, these findings indicate that CNT-modified membranes could positively impact the sustainability and performance of hollow fiber membranes being used in water purification.